Do you have a sneaking, yet unshakable, suspicion that your Web Analtyics Vendor is sometimes just trying to mess with you?

Guess what?

It's true!

All web analytics tools have a smattering of metrics and key performance indicators that were created just because someone decided it would be cute to add / subtract / multiply / divide some numbers.

Many of these don't pass the first sniff test and when if they do you are still left wondering: "What in God's name and all that is holy in this world am I supposed to action based on this metric?"

The answer?

Nothing.

With that gloriously upbeat set up let me tell you what we are going to cover today: Three metrics that are available in pretty much all "adult" web analytics tools. Daily, Weekly, Monthly Unique Visitors.

They are so common yet most people don't understand them well enough and fewer still realize how harmful these can be to your health even in day to day use.

So in this post we try to understand the most basic of the web analtyics basics, the Unique Visitor computation.

What's a Unique Visitor?

It is simple really. . . .

Technical Definition: Count of all the Unique cookie_id’s during a given time period.

English Definition: The first time someone visits your site a first party persistent cookie is set in their browser. This cookie lasts any where from several months to several years. Each time that person visits your site that cookie identifies them as the same browser.

Notice I said browser, not person. It is likely, but not always true, that each a unique visitor is a unique person.

Very predictably every 18 months or so the blogosphere goes wild with how accurate, or not, the Unique Visitor metric is. Much mud is thrown around. Indignations are foisted on the world. Name calling ensues.

Regardless of that Unique Visitors remains a valuable metric that used correctly, in place of Visits, measures success of your online marketing efforts.

Oh and your best weapon against ignorance? Education. See above post on Visitors. And this one: A Primer On Web Analytics Visitor Tracking Cookies. It covers cookies and deletion rates and other such yummy stuff. Read that and you have my word you'll be the smartest cookie in the room.

Each is trying to tell you something about Unique Visitors, yet if you pause and think about it, I mean really pause and think about it, you'll realize two of these are really bad for your health, and the third should be used with caution.

The core reason is that what looks attractive initially becomes progressively worse as you extend the time period. The Daily metric, so to speak, does not even last in value beyond two days!

So let's spend a second understanding this slightly yucky phenomenon.

Here's the data, from omniture.com, where WebTrends is used for tracking Visitors. . .

Now let's go measure the complex set of metrics that'll stare at you, let's say when you crack open Omniture or WebTrends (or pretty much any other competitive web analtyics tool).

The Web Analytics Unique Visitors Story:

Before that realize that what you see will depend on the time period you are looking at. [Arrrh!]

And before I really really jump in… you'll see a metric called Absolute Unique Visitor. I am going to use that as a proxy for how unique visitors should be computed correctly, regardless of what time period you are computing it for. Keep an eye on that number.

Looking at Month 1 and Week 1 at the end of Day One:

If you ran your reports at the end of day one here is what your analytics tool will report to you, with some delight and joy I might add. . .

The correct measure of unique is the Absolute Unique Visitors metric because it de-dupes the unique visitors across the entire time period you are reporting on.

Life lesson: Both Daily Unique Visitors and Weekly Unique Visitors numbers are totally really useless when you look across months. Use Monthly Unique Visitors with caution, knowing it is only de-duping for each month and then summing the number for each month.

If your tool provides Absolute Unique Visitors you are in luck because then you are getting true unique visitors across whatever arbitrary time period you choose.

Google Analytics provides you with the Absolute Unique Visitors metric.

[Update: In the new version of Google Analytics this metric is called Unique Visitors. Everything about it described is the same in terms of it providing a unique de-duped count, it's just called Unique Visitors. You'll find it in standard reports, and you can easily add it to any custom report. Try it!]

It will do that across set time periods, like the month of March (or any number of months). . .

or across arbitrary time periods, as Monday March 9th through Thursday March 19th. . .

It will dedupe the numbers when it reports to you, rather than adding the totals of each day, week or month.

Complex but bonus for Ninjas: Depending on which graph you look at, daily, weekly or monthly, it will intelligently compute the number for each time period and also show you the aggregate deduped number for that time period.

Fly in the otherwise rather healing ointment?

Google Analtyics does not compute Absolute Unique Visitors when you segment the data, when you use the Advanced Segmentation feature. Those of you who read the blog know my utter infatuation with segmentation, so you can easily understand how sad this makes me.

You can get Absolute Unique Visitors for segments by using the "create a filtered profile that just data for the segment" method and that works if you have forethought. But it is sub optimal, just like some "enterprise" web analytics vendors telling you that you can only segment if you tell them before the fact what you might want to segment later.

If these metrics are that sub optimal, why do web analytics vendors put us through this torture?

Simple: Compute power (translation: cost, for them).

It is very computationally intensive to calculate for you the true real (Absolute) Unique Visitor number across any arbitrary time period or across multiple weeks or months.

Increased computational intensity for the vendor means more processing time and higher costs.

So doing Daily, Weekly and Monthly counts (and then summing them up) is cheaper for them.

After the first vendor decided to do this, and there were no major outcry from Web Analytics Users (or even Ninjas!), others quickly followed.

For the more prevalent vendors in the space Google Analytics is one the rarest that provides the truly de-duped Absolute Unique Visitor metric (in aggregate, not segmented, boo!). Only time will tell when Google will buckle under the computation/cost weight and stop providing it true Absolute Unique Visitors.

[Update: Both NedStat and Xiti, two wonderful European companies do allow for computation of Absolute Unique Visitors out of their standard packages, no additional payment or gyrations required. Add Unica's NetInsight to that list as well! Hurray!!]

There are some vendors that will tell you that you can buy their more expensive data warehouse solutions (at an additional cost on top of what you pay today) and then compute Absolute Unique Visitors yourself. True. Ask for the cost. Ask if its really Absolute. If prudent, pay more. Regardless, be informed.

Long lesson.

But now you are truly at a Analysis Ninja black belt level of proficiency!

Now your turn.

Please share your comments / feedback / critique / hugs / non-hugs about this post. What does your tool do? How do you think we should improve things? What would you eliminate? What would you add? What did I miss?

Comments

Well thank you Avinash for making a big note of the fact that you cannot segment AUV in GA. I really hope they find a way. I experience the same "booo" with Funnel Visualization – would be awesome to be able to apply an Advanced Segment there.

I'm surprised you say that Google will buckle under the computation/cost weight and stop providing true Absolute Unique Visitors.

Perhaps it's because I'm not familiar with what it takes to provide this information, but I would think it would go the other way. Processing power is becoming cheaper over time. Also I would think that any web analytics company worth their salt who is charging (an arm and a leg in many cases) wouldn't want a free tool like GA to upstage them.

+ + + + +
NOTE: 1) I think you are exponentially hugely massively underestimating the amount of data GA needs to process each day. 2) Please know that I am just saying if every other vendor gave up on providing this metric, Absolute Unique Visitors, in their standard web analytics tool (Site Catalyst, WebTrends, Yahoo! Web Analytics etc) then maybe Google will follow. BUT. I am not saying it is happening or it will happen or should happen. : ) -Avinash.

Agree with you Avinash on the uselessness and dangers of aggregating Daily Uniques. And on trending, I would say that if someone really really feel the urge to trend DUVs :-) then do it for the incrementals – so in the example above, 3 DUV the first day, 2 DUV the second day, 1 DUV the third day and so on.

Also, on the case of unique visitors in general – if one is lucky enough to have a userid/sign-on/login etc. information for their site (even for a subset of their visitors), and they have the infrastructure where they are passing that into their WA tool – then I think they should leverage that and use that in synthesis with and complementing the cookie based counts.

Of course, there is always the KISS principle (Keep It Simple Stupid). I agree with you totally that just using the WA tool (and GA to get a leg up :-) ) and using the cookie based counts wisely can still provide one with useful information — so long as they understand all the caveats and assumptions involved. Or on the other extreme one can do some fancy number crunching and analytics using information from the WA tool and something like SAS or Tableau.

(I would like to cut down on the categories though :-) (from DUV, WUV, MUV, AUV etc. to just UV).)

As well as you we are too pretty sad about the AUV's non availability when using advanced segments.

The problem is that the work-around by using filtered profiles, don´t work well when you are firing events, because the events are not easily related to visits and is required too much computation power as well.

As you mentioned into the Ninja's Bonus when you look at the Visitor Trending -> Absolute Unique Visitors report into GA you have booth metrics: the Absolute Unique Visitors number for the whole period and the (un-duplicated) unique visitors number for every single day/week/month. Many people don't realize that if you add the unique visitors number across the whole period it differs from the AUV showed into report.

By the way, thanks for your conference into Buenos Aires, was such an inspiration for all us.

It saddens me to hear that you wonder how long it will be before GA takes away absolute unique visitors!

I've also had many "awwww"s as I've tried to get absolute unique visitors with segmentation to no avail. However, I always had faith that it would come someday, as GA seemed to be improving with each new release.

So with this post, the Web Evangelist himself, saying it probably will get worse, I'm truly saddened. Say it ain't so!

It is amazing that you can make the complicated so simple to understand Avinash. Wonderful post.

You were quite restrained though. For example our famous enterprise vendor only provides Daily Unique Visitors by default. Before I joined our company was reporting totals for daily uniques by Week and Month, which as you point out is complete garbage.

We had to pointedly ask for Weekly and Monthly Uniques and were told it could be "turned on" for us but would cost more in terms of the contract.

Many vendors continue this deceptive practice even now, after daily uniques have been debunked so thoroughly.

Very thought-provoking. This is an issue I go back and forth on and I'm constantly struggling with it.

Here are my issues:

1. Cookie deletion is only half the problem – different computers/browsers/devices are a big problem, too.

2. Going along with #1, although *we* understand the complexity of unique visitors, the people who demand these numbers probably don't (and explaining it gets you glassy-eyed stares!). My problem is with the name – unique visitors – which assumes we are talking about unique people.

AND since my good name is used in the example above, I feel almost obligated to respond :-)

Daily, Weekly and Monthly unique visitors was a great way of faking it for a while (as it is indeed more “expensive” to provide true visitor level segmentation). I was quite honestly impressed by GA launching with this way back (actually cried a bit on the inside as we were still a independent paid for vendor).

But I am happy to announce that upcoming version of Yahoo! Web Analytics, will indeed hold an amalgamation of the above three into ONE “Visitors” metrics.

Andrew: I think you are exponentially hugely massively underestimating the amount of data GA needs to process each day.

[+Nelson ] Please know that I am just saying if every other vendor gave up on providing this metric, Absolute Unique Visitors, in their standard web analytics tool (Site Catalyst, WebTrends, Yahoo! Web Analytics etc) then maybe Google will follow. BUT. I am not saying it is happening or it will happen or should happen. : )

Ned: Are you sure you are not putting lipstick on a pig by doing incremental trending? :)

Just teasing you!

There are a number of ways to ensure you are capturing the best possible dataset. Using first party cookies. Doing correlations with your login data. Even once in a while mashing it up and having a fight with your log file data.

Let's follow all the best practices, the data is meaningful and it helps make good decisions. No?

Jose: I do not want to shortchange my answer to your question about deletion rates etc, please see this post:

Shelby: I am sympathetic to the fact that the metric's name could be cuter.

That does not distract from the value of the underlying measurement when you collect the data using best practices (see reply to Ned above).

No metric in this world is a panacea.

Visits (sessions) is a wonderfully useful metric, it is everywhere and should be used to the fullest extent of the law!

Ignoring Unique Visitors means making a decision that pan-session behavior is not important and that is a very sub optimal strategy by anyone. Or that measuring Conversion Rates as "one night stands" is the way to do marketing. Sub-optimal (I am sure you would agree).

Visits can't replace Visitors, and vice a versa. Each holds a valuable insights, it is your job to identify what that is for your business (edu) and it is mine to do the same for my business.

Of course you know all this already, I am just restating the obvious. : )

Dennis: Hurray! Can't wait.

And now you have shown that a free "enterprise" tool will provide data / metrics that even paid "enterprise" tools can't match (yes yes they can match it if you spend an additional $$$,$$$.$$ on top of what you are already paying). Sorry could not resist.

Let's say I have excluded keywords in the non paid keywords report like kw1|kw2|kw3 via the box at the bottom.

When I look at the data monthly for a quarter it is like jan 1000, feb 1200, apr 1300. But when I look at the quarter in one go even though it should give me 3500 total, it doesn't add up to that – it is less.

I understand and know the logic behind UV counts as stated in the post but I couldn't pin point the reason for this.

AT Internet/ XiTi customers take benefit of this feature for many years now.
Whatever the time period you select in the calendar, our solution gives unique visitors number.

Yes you're right, an additional calculation is necessary, it takes a little time on long time period but you get data in Behaviour > Unique visitors > Site summary. And you can apply segmentation on this report…

Great discussion. Just want to add one more parameter: In a western country with very high computer density, like here in scandinavia, a great part of the users have at least 2 computers, at home, at work, and maybe a laptop, an Iphone, and a minipc… and, like me, have at least 3 different browsers in each PC … how many absolute unique users am I?

So we have removed focus from uniquness long time ago. A visit is still the most important business metric. By the way, when we can, we track logged in memberIDs and calculate a uniqueness for other traffic based on this.

This comment isn't totally related to this post (sorry!) but after searching Google for 1hr to no avail, I thought you might have the answer…

Do I count 'flashservices/gateway' (flash remoting) as a page visit? I think it's just a way of connecting to flash content already displayed on a page.. but am not totally sure. Do I count this metric or remove it?

This is a great post on a question that seems to surface over and over again. I agree with Ned that there is benefit in tracking unique visitor counts for incremental time periods, daily, weekly, etc (despite putting lipstick on a pig). However, one problem we run into is that our WA data is rolled up based on a 4-5-4 fiscal calendar (this was our choice to appease the finance gods, everything must map to the fiscal calendar). In this situation a 5-week month could falsely show a huge traffic boost over a 4-week month, etc. Just another thing we have to remember to educate folks on. Thanks again for another solid post.

“What in God’s name and all that is holy in this world am I supposed to action based on this metric?”

Hmmm. Wrong question. :-)

The question is typically phrased by senior management as (for info sites vs selling sites) "How many people visited?". The sometimes implied sub-question being "how many left happy and satisfied with our offerings".

Which in turn means that if a simple metric like Visitors, in whatever variation, has a downward trend, then action that *will* be applied is: This site isn't working anymore, shut it down; and you're now out of a job.

So, yes I agree from a tactical perspective, these broad brush metrics aren't useful. From a strategic perspective they're often the only ones that matter.
These metrics are a … simplistic proxy for the detail of page landings, bounce, seo etc etc etc etc. Treat them as such, and they are incredibly useful; powerful even. Ignore them – imho :-) – at your peril.

What about the daily trend of monthly or weekly unique visitors. In other words, plotting the monthly or weekly unique visitors for every day of the month or week.

Media sites I work for use it often, since it allows them to see how many new users they capture every day, in the context of the month (or the week).

In other words, it sort of answers the question: do we capture new users, or we are stuck with the same audience over and over again?

Looking at the daily trend of daily uniques can sort of do it, but I rather do it with the monthly/weekly metric, since visitors do not necessarily come back every day.

What do you think about it?

In my opinion, it's the only advantage I see about having the weekly and monthly pre-calculations as standard metrics you can trend daily. This is something I miss with Google Analytics (even though it's not at all a priority inmho, the use is very specific)

It is amazing that even in 2009, we could still learn a lot by zooming into individual metrics (unique visitors, conversion, pages per visit, avg time on site, etc.) and have a nice overview. I wish I had this article when I had to explain this concept using HBX when internal client wanted quarterly visitors…

Btw, thanks for sharing an article (including your old one) after I reminded you of a bitter article. I guess the bottom line is, there are so much learnings and reminders from topics including unique visitors to conversions (outcome per unique). Again, thanks for this great article on unique visitors and a heads up through your email.

Nit: The total in your example won't tie because it is possible, just to be a bit extreme, that the same 1000 people from Jan came again in Feb and Apr. In this case your Absolute Unique Visitor number would be 1500 (1000 from Jan, 200 from Feb and 300 from April).

Benoit: Thanks for adding, I totally forgot!

I have updated my blog post to clearly indicate that Xiti has this functionality (as does NedStat).

Ateeq: I can agree that if the assumptions you mention hold true then that might be value in trending the data.

My hope though is that the Web Analytics vendors will solve the core problem and allow all of us to use the right data better rather than having to make accommodations for sub optimal data that is shoved at us.

Scott: If other solutions did what Google Analytics, NedStat and Xiti do, allow you to create your own Absolute Unique Visitors across any arbitrary time periods, then your problem will go away.

It is certainly the right way to do things and my hope is more vendors will do that.

Steve: I am confused, but let me give it a try. . .

There is no People in Web Analytics. (Is that even grammatically correct?)

I would answer that question by giving a one min elevator pitch on what UV's are and what they measure. Unlike many I continue to believe in the value of using Unique Visitors (they are not the panacea, but they are not the dirty diaper as others have said).

Next if indeed the action taking is as extreme as the one you have suggested, based just on Visitors, then it might be time to look for another job because that kind of management will run any business to the ground? :)

Pere: If there are specific campaigns I am running to acquire new traffic (say I am going to plunk down $1 million to spend on FaceBook in the next 9 days) then I think there is value in looking at the daily unique visitor number trended over those 9 days (or those 9 days and the next 18 to catch the laggards).

But unless a stimuli like that exists the daily trend will always be a poor answer to the question: "are we capturing new visitors to our site".

As you correctly mention weekly is better, monthly is better still.

Not just because the data will be better but also because it will force the Ninja to do strategic analysis and not be a Squirrel and chase his / her tail by doing tactical analysis on daily data.

As part of our reporting for B2B web analytics – the most difficult aspect is to present the website visits data in the right context. The numbers really make no sense to the business and core marketing community. Yesterday I came up with this simple concept and thought to have it weighed by you ( just in case you happen to see this in the million chatter). Probably it is nothing new!
The website visits can we presented in 4 main clusters

1) Brand Recall Reorganization: Number of direct page visits can be categorized in this bucket. So any variation in these numbers would mean increase or decrease in brand recall.

2) Search Engine Mindshare: The total search traffic is a measure of the competitive visibility that my brandcompany has on the internet. It’s a measure for the SEO team and also for content creators. The index can be used by all teams to see how they are faring MoM on search engine prominence.

3) Brand Awareness: All website visits associated with campaigns can come under this tab. Marketing campaigns should also focus on creating awareness measured by unique visits from campaigns whether its Google, or email traffic. Leads though remain the primary campaign objective – though its difficult considering 6 to 24 months sales cycles.

4) Online PR: Any referral traffic could be reported as a matrix of sum total of all visits from social media visits, online press releases, columns and articles across portals.

This is just the first brain wave. Do you think it makes sense to explore it further.

Amazing Post, for a newbie analyst, things can't get clearer than this. Been dabbling with web analytics tools and I am amazed how each one is similar but yet so different and how we have to be careful with our insights.

Thanks for posting this. You could also take a simple Venn diagram approach to explain this concept. The absolute unique visitors are:

V(a) + V(b) – V(aUb) where V is the number of visitors, a is the first period and b is the second period. Absolute unique visitors are the visitors in period 1 plus visitors in period 2 minus the common visitors in period 1 and period 2.

You state at the top that Daily Unique Visitors are "bad for your health". I'm wondering about operations whose audiences are inherently short-lived, perhaps even 1-offs, e.g. Conventions, Concert Ticket vendors, Online Fundraising drives, American Idol polls. In these instances, a 48-hr window is all that matters, as repeats are mostly non-existent.

Why, oh why couldn't you have written this post a few years ago?! :-) I have a very clear memory of a frustrating, circular discussion with WebTrends back when I was still learning the ropes, because the support fellow I was talking with didn't even fully understand the calculation and storage of Uniques.

You nailed it, in that it's a matter of aggregation tables simply incrementing daily, weekly, monthly counts as a way to shortcut data storage and processing. So, they weren't able to de-dupe to get to absolute uniques. Once that lightbulb went on, I immediately wanted to run and yank all occurrences of the Daily Unique Visitors that our end-users were able to get to, because they were happily tripping along and looking at the "Total Daily Unique Visitors"…for the month. Egad!

As for @Sarah's comment (No. 35) — that's a little scary. On the one hand, yes, all web analysts have to understand that trend analysis trumps "perfect accuracy" in web analytics. BUT, this post is a great example where a metric can be off by an order of magnitude from "reality" and, thus, drive some pretty ugly decisions (memories of working with a client who bought a marketing automation tool largely based on a gross misunderstanding of the data they were getting from a log-based installation of Urchin with no bot/spider filtering at all…and the implementation of the tag-based marketing automation tool surfaced the mistake ).

1) "Extrapolations & Mathematics" – the most famous online panel for the use measures online behavior of 200 million Americans using a panel of 180k. Check what the number is for your panel.

2) Sampling Bias – the most famous online panel is banned from installing its "monitoring software" (pseudo-spyware) at pretty much all companies (work) and Universities etc, it is also intrusive in terms of data it collects so even most minorly web savvy folks won't install it.

In general Panel based data starts to get decent for sites that get more than 2 million Unique Visitors a month.

At the end of this post you'll see me talk more about Panel based methods:

In this case if you follow what's happening in the tables you'll quickly realize that the trends of these data will show crap. That's my worry.

If that can be accounted for then absolute numbers don't matter, trends do.

Hasan: There are certainly exceptions to the rule. But even in your scenario would you not want to measure how many Absolute Unique Visitors you got over the time period you had tickets on sale or were raising funds? My personal take would be that even in those scenarios knowing Daily Unique Visitors would serve no value.

For example let's take this egregious scenario. You announce a sale today. It is a one day sale. Tickets are only available for tomorrow. That's it.

So you could go back and say, how many unique visitors I got on that one day? That's a good question. You can answer it by choosing Absolute Unique Visitor metric for that one day. The presence of the Daily Unique Visitor metric adds little/no value even in this scenario, and of course is corrosive for all the other scenarios in the post.

This is an excellent explaination of the problem with our existing analytics packages.

Business (non analytics geeks)users look at something like "Daily Unique Visitors" and assume it is an accurate representation of individual people over that period of time. That is wrong on two fronts. One for the reasons you have shown. It is also wrong because cookies do not equal people.

There is a movement in the Web Analytics standards bodies to require any measurement of "unique visitors" to be based on some identification of real people. It is a lot more work to create that metric since you have to understand (discover) the relationship between people and cookies for your site. That is a major exercise to get that data but probably worth doing if unique visitors are that important to your business.

The current usage of "unique visitor" is really "unique cookie". Changing the name on reports would help if it resulted in calls from people who don't understand what it means. That creates the opportunity to educate the users of our data on that distinction. Some will be able to understand the issue and appreciate the difference. Others will not want to get into that level of detail but at least they were not misled by a false label.

This requires changing the names of the data item as it is displayed on reports. We don't always have that ability but we should be demanding it from the vendors who are accepting our money.

What's your take on the way Webtrends uses Dynamic Visitors, a measure that switches dynamically between Daily, Weekly, Monthly, Quarterly and Yearly Unique Visitors based on the time frame selected in the report?

Obviously there's still the potential for some double counting (particularly since any custom date range will be built by adding smaller date ranges together), so you've got to bear that in mind. But when we look at a week or a month or a year, and Webtrends provides the appropriate unique (de-duped) visitor number for that time period, that's a fairly worthwhile metric, isn't it?

Avinash, excellent post, as usual. Thank goodness that "Angie" person didn't get lumped into the example until the end, because she's a habitual cookie-deleter and would really mess up the numbers. Although I guess she wouldn't have messed up the DUV numbers because they're messed up anyway. ;-)

I'd like to point out that WAA Standard definitions do NOT recognize the concept of "daily unique visitors," etc. as described in your post. Just "unique visitors," and they aren't unique visitors unless they're de-duplicated over the reporting period,regardless of what that reporting period may be.

We can add Unica's NetInsight to your list of tools that does this calculation properly, de-duping over the requested date range.

I'd also like to point out that, although GA uses cookies for UV tracking, some of us track authenticated userids in other tools, along with cookies. And most of the for-pay tools have some sort of hierarchy where they'll substitute some other identifier for the cookie if it's blocked (session ID, IP/User Agent, etc.) and some will use those numbers to take a guess at "anonymous" unique visitors. So to address Ken's comment above: unique visitors and unique cookies are not the same thing. That may be true for some tools, but it's definitely not a universal truth.

Also to Ken's comment, there is *not* a movement in web analytics standards bodies to require tying back cookie information to people… at least not that I'm aware of. :) That movement is driven by the IAB, which sets *advertising* standards. They have different reasons for doing what they do, and they don't represent most of us who are doing web analytics for a living, only that part of your time when you might be wearing an advertising buyer/seller hat.

Avinash, I agree with you 10000% about measuring "people" — I just don't see it happening any time soon, and as a practitioner I don't want to tell people they aren't welcome at my company's websites unless they tell me who they are. If you know what you're doing, you can still make some valuable observations based on cookies. No, you don't know how many people are visiting, but you can indeed get some insight into cross-session behavior and loyalty trends.

The media industry is in love with daily, weekly, and monthly unique visitors. Probably because it mirrors what's available in external measurement offerings via comScore, etc. If taken on a trended daily/weekly/monthly granularity report, those breaks actually work quite well.

I totally agree with your "up in arms" comment about unique cookies. Who cares people! Get over it already! Use it as a tool, as a relative measure, don't use it, I don't care. There are more important things to worry about, like conversion.

Hi Avinash,
Thanks for a great column. Would you please say again, slowly and loudly, how one would go about creating a filtered profile to produce AUV? It is not on the pre-defined filters list, needless to say.
Thanks/Amy

I completely agree that uniques are misinterpreted if you aggregate them. However, they still provide tremendously value if you use "Average Daily Uniques" or "Average Monthly uniques" across many days or months.

For example, I could have a quarterly dashboard that shows average daily uniques during Q1, and watch how it grows compared to Q2.

Rich: I am sorry but I am unsure of what strategic or tactical value exists in looking at "average daily uniques" for one month.

As I mentioned in the post I can see how someone might report things like "during this week our Average Daily Uniques" were xyz.

But once you move beyond a week it is not very useful (far too much double counting and other stuff) and certainly for a month the underlying data is such a mush that it is not of very much value.

Many tools, excepting Google Analytics, by default tell you Average Monthly Uniques if you look at time period longer than a month (GA will still give you absolute unique visitors). In that sense you might not have much of a choice when you look beyond one month.

I use Omniture SiteCatalyst and it has the Yearly Unique Visitors metric available. Would you then recommend that we should almost always use this as the metric to measure traffic? This is essentially the same as Absolute Unique Visitors if the reporting timeframe is captured within the same calendar year, correct?

(Obviously, we run into duplication of visitors issue if we a report for a timeframe across multiple years.)

Rich: If you are reporting on a year time period or conveniently report on data from, say, Jan to April 2010 then you can run the report on May 1st (and make sure you run it on May 1st or you are out of luck) and use that number to report the count of unique visitors to your site during that time period.

Usually that is not convenient. You don't always want to report on YTD or just the year.

Consider these extremely common scenarios:

You probably want the count of unique visits from Jan to March 2010 (and you want that number any time, not just on April 1st).

Or you want the unique visitors for April & May 2010 because you ran a massive campaign and you want segmented (say Paid Search only) unique visitors.

Or you want unique visitors from Feb 15th to April 15th because it coincided with launch of your new products.

All of the above scenarios make the limited Monthly or Yearly unique visitor numbers from your analytics tool to not be of much value.

All of the above scenarios you can do with Google Analytics. You can get Unique Visitors for any arbitrary time period and you can get Unique Visitors for arbitrary time periods for any segment you want (simply create a custom report and apply any segment you want on the fly).

That is what you want.

Not to adapt to the tool rather adapt the tool to your business needs.

Please note that at an additional cost you can purchase more tools from Omniture like Discover 2 or Insight in addition to Site Catalyst then you can create a query that will allow you to do the above. You just can't do that with Site Catalyst.

I think I'm missing something and hope you can clarify: in your first paragraph directly above this post: why do I have to run the report on May 1? If I visited the site on Jan 3rd, and again on Apr 5th, and then again on May 6th……and say today is May 15th, why can't I still run the reporting timeframe of Jan-Apr 2010 today (on May 15) and still get accurate numbers? I'm still counted as 1 yearly unique visitor (during Jan-Apr 2010) which is equivalent to Absolute Unique Visitors. I don't see the importance of why must I run it on May 1, 2010?

The other examples do make sense though: say I wanted unique visitors from Feb 15 to Apr 15 (as in your example above) – I would NOT be counted as a unique visitor in this bucket for the Yearly Unique Visitors report if I came to the site prior to Feb 15 during the year since I would have been counted as a unique visitor prior to Feb 15. This unique visitor count will then be "under-reported" since the yearly unique visitor count records the "uniqueness" upon my first visit to the site during the year.

Thanks again for the help! Appreciate you being a thought leader and educator in the world of web analytics!

Marco: The statements you have expressed are overtly broad, even as they express some parts of the reality we all have to live with.

Unique Visitors can be tracked, and to an extent that the number is quite useful for most websites. On to your questions….

"a lot of people/companies clean their cookies frequently. When you come back to the site the web analytics tool thinks that you are a unique visitor."

It depends on the type of the website, but frequently is perhaps stretching things a bit too much. For some tech savvy sites, say slashdot, that have a unique type of audience the cookie deletion can be up to 30% or even more. But for most websites that is not the case, for first party cookies (if you are still using third-party cookies then may the lord save you! :)). For this blog cookie deletion is around 3%.

"you can use login accounts to measure unique visitors, but one or more people can you the accounts, so it's not 100% sure."

Yes you can, and you should use features like Analytics Custom Variables to track logged in and not logged in behavior.

But remember that even when login is mandatory (like with banks, not like amazon where it is not mandatory), a tiny percent of your site traffic will log in.

Which means that can't be your only method of collecting Unique Visitor data since you'll only be analyzing a tiny fraction of your website Visitors.

"One or more people can visit a website from one computer. These are all unique visitors but not measured like a unique visitor."

Yes this can happen, especially in countries like India and China where availability of computers is not as much as it should be. In many of these cases the browsers also flush all the cookies after each session (for the next person who will log in), which also is something to consider.

So depending on the country you have to be a bit more careful. This for example is much less of an issue in the US or EU. Either way if you want to put in the effort you can analyze your logs and your tag data and run analysis to get a feel for how much this issue bedevils you.

"Isn't it better to don't report about unique visitors at all?"

Perhaps in some cases.

But in most cases the data you collect is sufficient and reflects enough reality that it will be of value and you should use it.

We have far too much "quicke" mentality in Online Marketing. We simply shout "Convert!!", "Convert NOW!!!", "WHAT THE HELL ARE YOU WAITING FOR THIS IS YOUR FIRST VISIT WHY THE HECK DON'T YOU CONVERT ALREADY".

It is painful to read that I know. But that is how we do marketing today.

When we focus on optimizing our sites through analysis of Visits that is exactly the kind of mental model we are empowering. We are optimizing for Visits. The reality is short of buying Pez Dispensers people don't convert on the same visit, they might never convert.

I am a fan of being customer centric. Reporting Unique Visitors and using Unique Visitors in metrics like Conversion Rates (Orders/Unique Visitors) helps us focus on multi visit behavior. I like that.

As with all metrics in Web Analytics, Visits or Page Views or Time on Site, accuracy is relative and focusing on trends is far more impactful and the quest for 100% perfection is futile.

-Avinash.PS: One final way to check if measuring and analyzing Unique Visitors is right for your business…. Measure Visits to Conversion (/Purchase) reports in your web analytics tool. If you are really top heavy then you might get away with it, but if not then your Visits only focused analysis will yield undesirable results for your company.

I'm totally agree about this kind of analysis. But I think that we need to understand web as media, not just auctions, e-commerce and these things. The digital market wants to increase the advertisers investment. Unfortunately, the web is not e-commerce overall and how can we build safe measurements tools to understand what the advertisers needs, because brands can be developed on the web, a huge part without on line purchase just to communicate. If consumers will decide to buy this product next weekend on the real shopping center, should we not regard it?

After reading this overview I think I have a better understanding of how Unique visitors number is calculated. But what is the difference now in GA between "Visitors" and "Unique Visitors". I'm doing some custom reports for our sales team (they want to know monthly unique visitors to the site…), and I keep getting the Unique Visitors number that is higher than Visitors (holds true across all segments, including unsegmented "all visits"). Is there a glitch in GA? Which number is more reliable?

i have a question concerning the two metrics "visits" and "unique visitors" in google analytics (no filters, no segmentation). Most of the pages of our website have slightly more Visits than unique visitors. I think that is normal. But some pages have up 10 times more unique visitors than visits. How is that possible ? What are possible explanations? A problem with cookies or analytics code?

Peter: I'm assuming you are looking at the Page reports in GA and then looking at Visits and UV.

You would think that UV can never be greater than Visits, and that is true. But there are quirks. In GA Visits are counted on the first hit of a session. So if a page is not viewed as the first hit of a session it will increment the count of Visitors but not Visits. Hence, in some cases, you end up with Unique Visitors > Visits.

Optimally what you want to measure on your Page reports are: Page Views & Unique Page Views. That will give you the optimal view of the data (how many times was a page viewed, how many times was that page viewed by an individual during that visit).

Thank you for your explanation and the hint concerning the Page Views/ Unique Page Views!

An hour ago I found the specific solution of my page (my quirk): The reason that some visits weren't count as a visit is a "javascript/css expand menu". The GA Code is at the end of the page and everytime the user leave the page to another destination page GA dont count a visit. All Pages with such "javascript/css expand menu" have that problem and all pages without such "javascript/css expand menu" haven't that problem. Maybe I have to put the GA Code on top of the page…

[…] Analytics guru Avinash Kaushik explains what they are, and what the different types you hear about mean, in Standard Metrics Revisited: Daily, Weekly, Monthly Unique Visitors from his Occam’s Razor blog. It’s a long article, but straightforwardly-explained throughout, so do bear with it, and you’ll be rewarded with an understanding of a crucial concept. Most importantly, it will explain why “Daily”, “Weekly” and “Monthly” Unique Visitors are a misleading statistic in most everyday use, which you should avoid. […]

"Ok," your boss says, "I get that traditional marketing is increasingly ineffective and expensive. I also get that we have to try to get on this 'social media' thing, but…" and here's the question that strikes fear in every consultant's heart and in every would-be change agent's heart as well…

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Another “problems with analytics” post, this time from Kaushik: Standard Metrics Revisited: #6: Daily, Weekly, Monthly Unique Visitors. He gives a great run down on cookies, unique visitors, and how to the daily report is useless when looking at periods outside of a day.
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[…] Avinash Kaushik gives us the details on visitors and analytics. Read on, as his insights are of great help when digging around your various analytics tools. Get future posts sent to you free and automatically via email or RSS Feed ! Related Posts: […]

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Top line figures
According to Google Analytics we had 88,664 unique visitors and 285,522 page views in 2009. Looking at this monthly, as you can see we’re hovering around 10,000 monthly unique visitors:
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[…] a quick search though). Avinash Kaushik has a good breakdown of the unique visitor metrics here: http://www.kaushik.net/avinash/2…Also, comparing Analytics Vendors is tricky business as the numbers will never match. Take a look at […]

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Unique Visitors – I just like this one. I am curious how many new people we are getting into the site. If you want to read more, this guy had the topic nailed. http://www.kaushik.net/avinash/standard-metrics-revisited-6-daily-weekly-monthly-unique-visitors/
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